The present invention relates to a radio communication system used for communications performed between a stationary communication device and vehicular communication devices, preferably employed in an automatic toll collection system, and relates to arrangements of the stationary communication device and the vehicular communication device used in this communication system.
An electronically controlled toll collecting system comprises a stationary communication device placed at a predetermined position of a tollgate for performing radio communications with vehicular communication devices mounted on vehicles passing through the tollgate. According to such an automatic toll collection system, collection of toll can be performed without toller""s aid by exchanging data between the stationary communication device and the vehicular communication device.
This kind of electronically controlled toll collecting system usually provides a sound guidance (or voice guidance) for letting users know road information etc. To this end, the stationary communication device transmits sound data by radio wave. The vehicular communication device, mounted on a vehicle, receives the sound data transmitted from the stationary communication device and converts the received sound data into perceptible sounds through a speaker in a passenger compartment of the vehicle. Unexamined Japanese Patent Application No. 4-111195, published in 1992, discloses a conventional sound guidance system. For the radio communications performed between a stationary communication device and a vehicular communication device, a predetermined communication frame is used for transmitting communication data. In such a sound data transmission performed between the stationary communication device and the vehicular communication device, there is a possibility that a huge amount of sound data cannot be transmitted by a single communication frame. To solve this problem, it is preferable to use a plurality of separate communication frames for transmitting the massive sound data. However, the vehicular communication device may fail to receive all of the separate communication frames. This will result in an inaccurate sound guidance.
An object of the present invention is to provide a reliable radio communication system used for communications between a stationary communication device and vehicular communication devices. Another object of the present invention is to provide arrangements of the stationary communication device and the vehicular communication device used in this communication system.
In order to accomplish this and other related objects, a first aspect of the present invention provides a communication system comprising a stationary communication device placed at a predetermined position and forming a communication area covering vehicles traveling on a road, and at least one vehicular communication device mounted on a vehicle for communicating with the stationary communication device when the vehicle enters in the communication area. The stationary communication device divides sound guidance data into a plurality of sound data blocks of predetermined communication frames and transmits the divided sound data blocks successively. The vehicular communication device receives the divided sound data blocks transmitted from the stationary communication device, and requests the stationary communication device to transmit specific sound data block again when the vehicular communication device fails to receive this specific sound data block, thereby issuing a sound guidance using the received sound data blocks including the specific sound data block transmitted again.
Preferably, the vehicular communication device includes a sound data storage means for storing a predetermined number of sound data beforehand, and the stationary communication device transmits a designation signal in addition to the divided sound data blocks so that the vehicular communication device reads particular sound data from the sound data storage means in response to the designation signal. An index number may be attached to each sound data stored in the sound data storage means of the vehicular communication device. In this case, the stationary communication device transmits the designation signal including an index number corresponding to the particular sound data. To reduce a data transmission amount, it is effective to store frequently or commonly used sound guidance information in the sound data storage means of the vehicular communication device.
Preferably, the stationary communication device transmits display data paired with corresponding sound data blocks, and the vehicular communication device comprises a display unit for displaying contents of the sound data blocks based on the display data paired with the sound data blocks.
Preferably, the stationary communication device and the vehicular communication device comprise a bandwidth limiting circuit which limits a frequency band of communication data for modulating a carrier wave used in radio communications performed between the stationary communication device and the vehicular communication device. The bandwidth limiting circuit may convert a rectangular waveform signal of digital communication data into a sine waveform signal.
Preferably, sound data are compressed by sampling characteristic points together with corresponding time information to create a polynomial representing a time variation of the sound data.
Alternatively, a plurality of phonemes are prepared beforehand and a sound is created by multiplying respective phonemes with appropriate parameters and adding the multiplied phonemes.
It is preferable that the vehicular communication device analyze missing sound data based on already received sound data and selectively issue a sound guidance or a display guidance according to the analysis.
To check any missing sound data, it is preferable that the divided sound data blocks are referred by sequential numbers.
A second aspect of the present invention provides a vehicular communication device mounted on a vehicle for communicating with a stationary communication device, comprising a receiving means for receiving divided sound data blocks successively transmitted from the stationary communication device, a request means for requesting the stationary communication device to transmit specific sound data block again when the specific sound data block is not received successfully, and a sound generating means for generating a sound in a compartment of the vehicle based on the received sound data blocks including the specific sound data block transmitted again.
Preferably, the vehicular communication device further comprises a temporary data storage means for temporarily storing the divided sound data blocks successively transmitted from the stationary communication device, and the sound generating means issues the sound based on the sound data blocks stored in the temporary data storage means. The sound generating means has a function of reissuing the sound based on the sound data blocks stored in the temporary data storage means.
The vehicular communication device may further comprise a sound output terminal connectable to an external speaker provided in the compartment of the vehicle. Preferably, a built-in speaker of the vehicular communication device causes no sound when the external speaker is connected to the sound output terminal. The external speaker may be a speaker of an external audio component. In this case, a sound output switcher is provided between the sound output terminal and the external audio component for selecting sound data sent to the external speaker. For example, the sound output switcher comprises a sound signal detecting circuit for detecting a sound signal generated from the sound output terminal, and a switching unit for supplying the sound signal to the external speaker when the sound signal detecting circuit detects the sound signal. To listen to a sound guidance easily, a sound signal sent from the sound output terminal to the external speaker can be enlarged than a sound signal sent from the external audio component to the external speaker.
A third aspect of the present invention provides a stationary communication device placed at a predetermined position for forming a communication area to communicate with a vehicular communication device mounted on a vehicle entering in the communication area; comprising a sound data transmitting means for dividing sound guidance data into a plurality of sound data blocks of predetermined communication frames and transmitting the divided sound data blocks successively to the vehicular communication device, and a missing data transmitting a means for transmitting specific sound data block again in response to a request returned from the vehicular communication device that fails to receive this specific sound data block.
A fourth aspect of the present invention provides a communication system comprising a stationary communication device placed at a predetermined position and forming a communication area to transmit sound data to vehicles traveling on a road, and at least one vehicular communication device mounted on a vehicle for receiving the sound data transmitted from the stationary communication device when the vehicle enters in the communication area. The vehicular communication device includes a sound data storage means for storing a predetermined number of sound data beforehand, and the stationary communication device transmits a designation signal in addition to the sound data so that the vehicular communication device reads particular sound data from the sound data storage means in response to the designation signal.